Built-in gutters are a favorite design feature among many architects. And that’s great: Properly installed, built-in gutters can provide a lifetime of trouble-free service.
However, built-in gutters expose a building to higher risk of water intrusion than any exposed-type gutter. When leaks occur in built-in gutters, the water is likely to intrude directly into the building.
The built-in nature of hidden gutters requires exemplary attention to critical construction details such as:
- Using corrosion-resistant materials
- Ensuring that all joints are lapped, riveted, and soldered
- Using continuous supports
- Applying long-lasting underlayments
- Paying particular attention to expansion control
- Ensuring that the front edge is a minimum of one inch lower than the back edge
For the best built-in gutter design, soldered seams are always better than using sealants. Locate downspouts in a manner that minimizes or eliminates the need for expansion joints. use continuous cleat and drip edges along the front, and extend waterproof membranes at least 24-in. behind wall lines in ice dam areas.
The construction and installation of low-slope specifications is problematic. It can be difficult for contractors to install a low-slope gutter so that no points along the gutter hold water. Just the variance caused by normal “oil canning” along the bottom profile of the gutter can counter the slope that is typically measured along the gutter’s upper/outer edge.
Minor “puddles” of standing water aren’t a problem unless the depth of the standing water exposes the gutter to damage from the expansion of freezing water. Where freezing water might be an issue, a bottom profile with a 45-degree turn in the back of the profile provides additional safety.
The old adage—out of sight, out of mind—too often applies to built-in (hidden) gutters. If hidden gutters are specified, call attention to the need for regular inspections by the owner to remove debris and to make sure that gutters and downspouts are kept clear.
Built-in gutter design and construction are covered in detail in the first chapter of the “Architectural Sheet Metal Manual.” from the Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA). To order, call SMACNA’s Publications Department at (703) 803-2989 or visit www.smacna.org/bookstore